Multi-junction light-emitting diode and method for making the same

Abstract

A multi-junction light-emitting diode (LED) includes a first epitaxial structure, a second epitaxial structure and a tunnel junction structure disposed therebetween. The tunnel junction structure includes a In z Al X1 Ga 1−X1 As highly doped p-type semiconductor layer wherein z ranges from 0 to 0.05, a Al X2 Ga 1−X2 As first composition graded layer wherein X2 is greater than 0 and less than X1, a Ga Y In 1−Y P highly doped n-type semiconductor layer and a Al X3 Ga 1−X3 As second composition graded layer that are sequentially disposed on the first epitaxial structure in such order. A method for making the abovementioned multi-junction LED is also disclosed.

What is claimed is: 
     
       1. A multi-junction light-emitting diode (LED), comprising a first epitaxial structure, a second epitaxial structure, and a tunnel junction structure disposed between said first epitaxial structure and said second epitaxial structure, said tunnel junction structure including:
 a highly doped p-type semiconductor layer that is made of a material represented by In z Al X1 Ga 1−X1 As, z ranging from 0 to 0.05; 
 a first composition graded layer that is disposed on said highly doped p-type semiconductor layer and that is made of a material represented by Al X2 Ga 1−X2 As, X2 being greater than 0 and less than X1; 
 a highly doped n-type semiconductor layer that is disposed on said first composition graded layer opposite to said highly doped p-type semiconductor layer and that is made of a material represented by Ga Y In 1−Y P; and 
 a second composition graded layer that is disposed on said highly doped n-type semiconductor layer opposite to said first composition graded layer and that is made of a material represented by Al X3 Ga 1−X3 As. 
 
     
     
       2. The multi-junction LED of  claim 1 , wherein in said highly doped p-type semiconductor layer, X1 is greater than 0 and not greater than 0.8. 
     
     
       3. The multi-junction LED of  claim 1 , wherein said highly doped p-type semiconductor layer has a doping concentration not less than 1×10 19  cm −3 . 
     
     
       4. The multi-junction LED of  claim 1 , wherein said highly doped p-type semiconductor layer is doped with carbon at a doping concentration ranging from 1×10 19  cm −3  to 2×10 20  cm −3 . 
     
     
       5. The multi-junction LED of  claim 1 , wherein said highly doped p-type semiconductor layer has a thickness ranging from 10 nm to 100 nm. 
     
     
       6. The multi-junction LED of  claim 1 , wherein in said highly doped n-type semiconductor layer, Y ranges from 0.45 to 0.7. 
     
     
       7. The multi-junction LED of  claim 1 , wherein said highly doped n-type semiconductor layer has a doping concentration not less than 1×10 19  cm −3 . 
     
     
       8. The multi-junction LED of  claim 1 , wherein said highly doped n-type semiconductor layer is doped with tellurium at a doping concentration ranging from 1×10 19  cm −3  to 2×10 20  cm −3 . 
     
     
       9. The multi-junction LED of  claim 8 , wherein said highly doped n-type semiconductor layer is further doped with silicon at a doping concentration ranging from 5×10 18  cm −3  to 2×10 19  cm −3 . 
     
     
       10. The multi-junction LED of  claim 9 , wherein in said highly doped n-type semiconductor layer, the doping concentration of tellurium to the doping concentration of silicon is in a ratio ranging from 5:3 to 2:1. 
     
     
       11. The multi-junction LED of  claim 1 , wherein said highly doped n-type semiconductor layer has a thickness ranging from 10 nm to 100 nm. 
     
     
       12. The multi-junction LED of  claim 1 , wherein in said first composition graded layer, X2 gradually decreases in a direction from said highly doped p-type semiconductor layer toward said highly doped n-type semiconductor layer. 
     
     
       13. The multi-junction LED of  claim 12 , wherein X2 linearly decreases in a direction from said highly doped p-type semiconductor layer toward said highly doped n-type semiconductor layer. 
     
     
       14. The multi-junction LED of  claim 1 , wherein said first composition graded layer is a p-type semiconductor layer which is doped with carbon at a doping concentration ranging from 1×10 19  cm −3  to 5×10 19  cm −3 . 
     
     
       15. The multi-junction LED of  claim 1 , wherein said first composition graded layer has a thickness ranging from 10 nm to 50 nm. 
     
     
       16. The multi-junction LED of  claim 1 , wherein in said second composition graded layer, X3 gradually increases in a direction away from said highly doped n-type semiconductor layer. 
     
     
       17. The multi-junction LED of  claim 16 , wherein X3 linearly increases in a direction away from said highly doped n-type semiconductor layer. 
     
     
       18. The multi-junction LED of  claim 1 , wherein said second composition graded layer is an n-type semiconductor layer which is doped with tellurium at a doping concentration ranging from 1×10 19  cm −3  to 5×10 19  cm −3 . 
     
     
       19. The multi-junction LED of  claim 1 , wherein said second composition graded layer has a thickness ranging from 10 nm to 50 nm. 
     
     
       20. The multi-junction LED of  claim 1 , wherein each of said first and second epitaxial structures independently emits an infrared light having a wavelength ranging from 760 nm to 1100 nm. 
     
     
       21. A method for making a multi-junction LED, comprising the steps of:
 (A) forming a first epitaxial structure, 
 (B) forming a tunnel junction structure on the first epitaxial structure, wherein the tunnel junction structure includes:
 a highly doped p-type semiconductor layer that is made of a material represented by In z Al X1 Ga 1−X1 As, z ranging from 0 to 0.05; 
 a first composition graded layer that is disposed on the highly doped p-type semiconductor layer and that is made of a material represented by Al X2 Ga 1−X2 As, X2 being greater than 0 and less than X1; 
 a highly doped n-type semiconductor layer that is disposed on the first composition graded layer opposite to the highly doped p-type semiconductor layer and that is made of a material represented by Ga Y In 1−Y P; and 
 a second composition graded layer that is disposed on the highly doped n-type semiconductor layer opposite to the first composition graded layer and that is made of a material represented by Al X3 Ga 1−X3 As, and 
 
 (C) forming a second epitaxial structure on the tunnel junction structure opposite to the first epitaxial structure.